Process for calcining coke

Abstract

A process for calcining green coke containing water and combustible volatile matter and obtained by a delayed coking process in three or more stages of heating furnaces which are connected in series, and the control of the temperature and the adjustment of the atmosphere in the respective furnaces can be independently carried out, which process comprises carrying out, in respective furnaces in the indicated order, the steps of: (a) evaporating the water contained in the green coke, and drying and pre-heating the coke; (b) distilling off and burning the volatile matter from the dried coke; and (c) heating and calcining the coke from the step (b). Because each furnace can be controlled independently from the other furnaces in the above described process, it is possible to produce high-grade coke without process difficulties such as the loss of the coke by combustion and the formation of coke ring.

We claim: 
     
       1. A process for calcining green coke containing substantial amounts of water and combustible volatile matter obtained by a delayed coking process in three rotary kilns which are connected in series and wherein the control of the temperature and the adjustment of the atmosphere can be independently carried out, which process comprises carrying out, in the respective kilns in the indicated order, the steps of: (a) evaporating the water contained in the green coke, and drying and pre-heating the coke to give a final coke temperature in the range of from 350° to 400° C. with off-gases from steps (b) and (c) mentioned hereinbelow,   (b) distilling off and burning the volatile matter of the dried coke through a second rotary kiln in an oxidation atmosphere for about 30 to 60 minutes to give a final coke temperature of 800° to 980° C. with air flowing concurrently with the coke,   (c) heating and calcining the coke from the step (b) at a temperature of 1,200° to 1,500° C. for 10 to 30 minutes by using as the heating medium a combustion gas obtained by burning fuel at the outlet of the third rotary kiln.   
     
     
       2. A process as claimed in claim 1, wherein the retention time of the first furnace is 10 to 30 minutes.   
     
     
       3. A process as claimed in claim 1, wherein the green coke is heated in the first furnace by a hot gas at a temperature of 1,100° to 1,300° C. having issued from the second and the third furnaces and flowing counter currently with the green coke, and the hot gas is cooled to a temperature of 500° to 700° C. 
     
     
       4. A process as claimed in claim 3, wherein air is indirectly heated by the hot gas from the first furnace to form pre-heated air. 
     
     
       5. A process as claimed in claim 3, wherein the pre-heated air is branched, and one portion thereof is charged into the second furnace together with the pre-heated coke from the first furnace in a parallel flow to use said air for burning the volatile matter contained in the pre-heated coke, the remaining portion of the pre-heated air being used to burn fuel at the outlet end for discharging coke of the third furnace, the resulting combustion gas being used to calcine the coke in the third furnace. 
     
     
       6. A process as claimed in claim 4, wherein at the start of the operation, auxiliary fuel is burned at the inlet end for introducing coke in the second furnace to heat the coke from the first furnace to a temperature at which the volatile matter is burned. 
     
     
       7. A process as claimed in claim 1, wherein said green coke contains 7 to 10% by weight of water and 6 to 10% by weight of volatile matter.